This section provides background information related to the present disclosure which is not necessarily prior art.
This specification describes a system that forms and joins sheet material and, in particular, a hemming device and method of use at an assembly-line station, which is considered on-line, where it is sometimes preferred versus off-line where an added station and event is expensed. The assembly-line station environment presents partially assembled panels oriented in vehicle position, which is reversed relative to off-line hemming. A hemming tool assembly having a roller hemming unit operates in this environment with unlimited hem flange orientation without physical attachment to a counter-pressure device, and with the flexibility to manage multiple vehicle body model shapes at a single assembly-line station.
One of the earliest operations required in the history of automobile assembly was on-line joining of panels to form a variety of body assemblies to build up a vehicle body. On-line welding pinches the panels together between two welding-tips via a common jaw, then a weld current is induced until securely joined. Similarly, on-line roller hemming pinches the panels together between two rollers via a common jaw, then multiple passes are made until securely joined. Welding and hemming are both widely used. Welding is the most popular method though it is not often used on class-a surfaces due to marking, while hemming is intended for class-a joining. An example of off-line hemming may be found in U.S. Pat. No. 5,454,261 issued on Oct. 3, 1995 to Campian for HEMMING MACHINE AND METHOD OF OPERATION. Examples of known on-line hemming are set forth in U.S. Pat. No. 7,017,268 issued on Mar. 16, 2006 to Lang for SEAL REFORMING METHOD AND APPARATUS, and U.S. Pat. No. 7,500,373 issued on Mar. 10, 2009 to Quell for FLANGING DEVICE AND FLANGING METHOD WITH COMPONENT PROTECTION.
While the above-referenced patents provided advancements in the state of the art of machines for joining two panels together, opportunity for design and feature improvement remained available. One of the difficulties of known on-line panel joining devices has to do with backing up the pressures induced to the hem flange to prevent panel deformation. As is known in the art, pinch rollers provide pressure to a pair of rollers, but are difficult to program and have angular manipulation restraints. The restraint on angular manipulation arises from the use of a common jaw supporting both rollers which results in an inability to make complex panel shapes or bow-tie-flanges—e.g., final flanges that vary the completeness of the folded flange from closed to partly open to fully open which are common to automotive assemblies.
Existing off-line hemming systems possess a stable and rigid lower anvil that is generally mounted horizontally with the floor. The incoming assembly is unattached to other assemblies allowing free and easy handling and orientation. The assembly drops onto the anvil from above, gravity assisted, with the class-a facing down on the anvil and the flanges to be hemmed facing up and out. The hemming head has open real estate to manipulate while pushing and driving the flange downward into the anvil. On the other hand, on-line hemming systems orient the part with the class-a facing outboard and the hemming work is done vertically to the floor which makes it impossible to use conventional off-line hemming heads and rollers due to the orientation of the part. There is also little or no room for the robot knuckle to manipulate from the inside of the vehicle to the outside, as the hemming forces dictate. Even if the robot knuckle has enough room to work from the inside out, the class-a metal would distort from the pressures required to hem.
To date there is no way to use a single conventional roller hemming tool in an on-line hemming station. On-line hemming has been performed using non-conventional pinch rollers that use a counter-pressure roller. It is a limited technique that does not yield high-quality flanges. The main issues are that the pressures applied are angular to the surface during the prehem passes, which have the greatest effect on the final hem quality. During prehem, the pinch rollers form a v-shape and the robotic paths attempt to compensate the angular skid of both paths simultaneously. Reviewing after a pinch rolling operation directly on class-a reveals scratches and skid marks evident on the class-a surface.
To protect the class-a surface from this damage, a known protective cover is used between the counter-pressure wheel and the class-a surface. It protects the class-a by having the counter-pressure wheel travel along a machined race track on the face of the cover, and at the same time limits the rotational freedom of the hemming tool as it is locked into following the track exactly. Reprogramming different angles within the path requires substantial re-tooling of the machined race track. To change angles if a path needs reprogramming requires the cover's surface to be welded and re-cut to the new angle. Abrupt changes to the attack angles are known to be done with pinch rollers by physically adding additional rollers to the head assembly.
Unfortunate features of pinch-rollers include: (a) the flange-side roller requires an attachment to a jaw with a direct relationship to a back-side counter-pressure roller also attached to same jaw for countering the applied force of the flange-side roller to prevent panel deformation; (b) the pinch rollers are locked in relationship to one another and have no opportunity to be quickly swapped out by rollers of different shapes to more robustly hem different panel shapes; (c) the pinch rollers possess an inherent inability to adjust the yaw, pitch or roll of the rollers during the hemming process to more robustly follow different panel shapes and associated attack angles; (d) the program path of both rollers are locked together via the jaw, and have extreme programming limitations of the counter-pressure roller with relationship to the panel surface and/or backer track; and (e) the hem attack angle is locked and non-adjustable, changing this requires introducing multiple rollers, each locked to different angles.
Another prior approach to address on-line hemming is the use of sliders, which offer low quality and little flexibility to manage multiple vehicle body model shapes on the same assembly-line.
Prior approaches to address on-line hemming have failed to overcome the aforementioned problems. Accordingly, an on-line hemming system that captures all the flexibility that off-line systems exhibit remains wanting.